Velvetbean(Mucuna pruriens (L.) DC. var. utilis oi Stizolobium deeringianum Piper et Tracy, synonymbut now not recommended)1>2) is a tropical legume, cultivated as green manureor as a cover crop. Velvetbean leaves are used as fodder, the seeds as food, and the seeds and stems as medicine in Africa and China.3) The yield of seeds reaches 1.5-2t/ha, and offresh leaves and stems comestc 20-30t/ha, this crop being one of the most productive ir the world.Mucuna pruriens has been reported to increase the graminaceous crop yield in mixed culture, but to smother notorious weeds such as nutsedge (Cyperus spp.) and alang-alang (Imperata cylindrica).4) We have screened allelopathic plants with seedling growth tests, and evaluated velvetbean as the most promising candidate.5 Field tests showed the least weed population in velvetbean stands in contrast to the stands of other crops and fallow conditions.6) A dwarf species of velvetbean, cv. ana (a cultivar in Brazil), was used. For the bioassay,5) ten lettuce seeds were placed in 4.5cm diameter Petri dishes containing 1.0ml oi the test solution on Whatman No. 1 filter papers, and were incubated at 25°C in the dark. The germinated seeds were counted and the hypocotyl and radicle growth was measuredon the 4th day. Fresh fully expanded leaves and roots of velvetbean were extracted with 80%etha-nol. The acid fraction of the extract inhibited the growth of lettuce seedlings. This fraction was subjected tc silica gel column chromatography (from 100% benzene tc 100% ethylacetate with a 5% step up, then to 100% methanol with a 5% step up, the active fraction being ethylacetate-benzene (50 : 50)), and HPLC with an ODS column (concave gradient from 1 5% methanol in 2% acetic acid to 99% methanol in 2% acetic acid), and the major inhibitor was identical to L-3,4-dihydroxyphenylalanine

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